Method and apparatus for recovering license plate information from an image

Abstract

Some aspects of the invention relate to a mobile apparatus including an image sensor configured to convert an optical image into an electrical signal. The optical image includes an image of a vehicle license plate. The mobile apparatus includes a license plate detector configured to process the electrical signal to recover information from the vehicle license plate image.

What is claimed is: 
     
       1. A mobile apparatus, comprising:
 an image sensor configured to capture an optical image including an image of a vehicle license plate; and 
 a license plate detector configured to:
 identify and crop, by a processor, one or more object images from the captured optical image with each of said one or more cropped object images comprising a candidate vehicle license plate image having a plurality of alphanumeric characters, 
 score, by the processor, each of said cropped one or more object images based on a probability that the respective cropped object image comprises the vehicle license plate image, wherein each of the cropped one or more object images is scored by:
 providing a rectangular fitting around each character of the plurality of alphanumeric characters, 
 fitting a line to a center of the respective rectangular fittings of each pair of the plurality of alphanumeric characters, 
 for each fitted line, summing a distance of all other respective rectangular fittings to the respective fitted line, 
 selecting the respective pair of alphanumeric characters corresponding to the respective fitted line with a smallest summed distance of all of the fitted lines as a text baseline for the candidate vehicle license plate image, 
 computing a score for the candidate vehicle license plate image having the selected text baseline based at least on the rectangular fitting around each of the alphanumeric characters, relative positions of each of the alphanumeric characters relative to each other within the respective cropped object image and a calculated slope of the fitted line for the selected pair of alphanumeric characters, and 
 
 recover, by the processor, information relating to the vehicle license plate in
 response to the calculated score of the candidate vehicle license plate image confirming that the respective cropped object image corresponds to the vehicle license plate. 
 
 
 
     
     
       2. The mobile apparatus of  claim 1 , wherein the license plate detector is further configured to select one of said one or more of the cropped object images based on each object image's score. 
     
     
       3. The mobile apparatus of  claim 2 , wherein the license plate detector is further configured to recover the information from the selected one of said one or more of the cropped object images. 
     
     
       4. The mobile apparatus of  claim 1 , wherein the license plate detector is further configured to process the captured optical image to dewarp at least one of said one or more of the object images. 
     
     
       5. The mobile apparatus of  claim 1 , further comprising a display and a rendering module configured to render the optical image to the display and overlay a detection indicator on each of said one or more of the cropped object images in the optical image. 
     
     
       6. The mobile apparatus of  claim 1 , further comprising an image filter configured to:
 apply a set of filter parameters to the captured optical image; and 
 dynamically adjust the parameters based on at least one of color temperature, ambient light, object image location, and the location of the apparatus. 
 
     
     
       7. The mobile apparatus of  claim 1 , wherein the license plate detector is further configured to apply a straight line through each of the pairs of alphanumeric characters within each respective cropped object image, such that at least one pair of alphanumeric characters is discarded as a candidate vehicle license plate image if the straight line through the respective pair of alphanumeric characters has a non-zero slope relative to a horizontal direction of the candidate license plate. 
     
     
       8. A mobile apparatus, comprising:
 an image sensor configured to capture an optical image, wherein the captured optical image comprises a plurality of object images, and wherein one of the plurality of object images comprises an image of a vehicle license plate; and 
 a license plate detector configured to:
 identify and crop, by a processor, one or more object images from the captured optical image with each of said one or more cropped object images comprising a candidate vehicle license plate image having a plurality of alphanumeric, 
 score, by the processor, each of said cropped one or more object images based on a probability that the respective cropped object image comprises the vehicle license plate image, wherein each of the cropped one or more object images is scored by:
 providing a rectangular fitting around each character of the plurality of alphanumeric characters, 
 fitting a line to a center of the respective rectangular fittings of each pair of the plurality of alphanumeric characters, 
 for each fitted line, summing a distance of all other respective rectangular fittings to the respective fitted line, 
 selecting the respective pair of alphanumeric characters corresponding to the respective fitted line with a smallest summed distance of all of the fitted lines as a text baseline for the candidate vehicle license plate image, 
 computing a score for the candidate vehicle license plate image having the selected text baseline based at least on the rectangular fitting around each of the alphanumeric characters, relative positions of each of the alphanumeric characters relative to each other within the respective cropped object image and a calculated slope of the fitted line for the selected pair of alphanumeric characters, and 
 
 recover, by the processor, information relating to the vehicle license plate in response to the calculated score of the candidate vehicle license plate image confirming that the respective cropped object image corresponds to the vehicle license plate. 
 
 
     
     
       9. The mobile apparatus of  claim 8 , wherein the license plate detector is further configured to process the captured optical image to dewarp said one of the object images prior to recovering the information. 
     
     
       10. The mobile apparatus of  claim 8 , further comprising a display and a rendering module configured to render the optical image to the display and overlay a detection indicator on each of the plurality of object images. 
     
     
       11. The mobile apparatus of  claim 10 , wherein the rendering module is further configured to overlay a first detection indicator over said one of the plurality of object images and a second detection indicator over the other object images of said plurality of object images. 
     
     
       12. The mobile apparatus of  claim 11 , wherein the rendering module is further configured to cause the first detection indicator to appear visually different from the second detection indicator on the display. 
     
     
       13. The mobile apparatus of  claim 8 , wherein the license plate detector is further configured to process the captured optical image to score each of the plurality of object images based on a probability that the each of the plurality of object images comprises the vehicle license plate. 
     
     
       14. The mobile apparatus of  claim 13 , wherein the license plate detector is further configured to select said one of the plurality of object images based on the selected object image's score. 
     
     
       15. A mobile apparatus, comprising:
 an image sensor configured to capture an optical image comprising an image of a vehicle license plate; 
 a display; 
 a rendering module configured to render the captured optical image to the display; 
 an image filter configured to apply one or more filter parameters to the captured optical image based on at least one of color temperature of the image, ambient light, and motion of the apparatus; and 
 a license plate detector configured to:
 identify and crop, by a processor, one or more object images from the captured optical image with each of said one or more cropped object images comprising a candidate vehicle license plate image having a plurality of alphanumeric characters, 
 score, by the processor, each of said cropped one or more of the object images based on a probability that the respective cropped object image comprises the vehicle license plate image, wherein each of the cropped one or more object images is scored by:
 providing a rectangular fitting around each character of the plurality of alphanumeric characters, 
 fitting a line to a center of the respective rectangular fittings of each pair of the plurality of alphanumeric characters, 
 for each fitted line, summing a distance of all other respective rectangular fittings to the respective fitted line, 
 selecting the respective pair of alphanumeric characters corresponding to the respective fitted line with a smallest summed distance of all of the fitted lines as a text baseline for the candidate vehicle license plate image, 
 computing a score for the candidate vehicle license plate image having the selected text baseline based at least on the rectangular fitting around each of the alphanumeric characters, relative positions of each of the alphanumeric characters relative to each other within the respective cropped object image and a calculated slope of the fitted line for the selected pair of alphanumeric characters, and 
 
 recover, by the processor, information relating to the vehicle license plate in response to the calculated score of the candidate vehicle license plate image confirming that the respective cropped object image corresponds to the vehicle license plate; 
 
 wherein the rendering module is further configured to overlay a detection indicator on the displayed optical image to assist a user in positioning the apparatus with respect to the optical image in response to a signal from the image filter; and 
 wherein the rendering module is further configured to provide an alert to the display when the license plate detector fails to recover the vehicle license plate information. 
 
     
     
       16. The mobile apparatus of  claim 15 , wherein the license plate detector is further configured to process the captured optical image to dewarp at least one of said one or more of the plurality of object images. 
     
     
       17. A computer program product for a mobile apparatus having an image sensor configured to capture an optical image, the captured optical image including a plurality of object images, the computer program product comprising:
 a non-transitory machine readable medium comprising code to:
 select and crop, by a processor, said one of the object images based on the captured optical image, wherein each of said one or more cropped object images comprises a candidate vehicle license plate image having a plurality of alphanumeric characters; 
 provide a rectangular fitting around each character of the plurality of alphanumeric characters; 
 fitting a line to a center of the respective rectangular fittings of each pair of the plurality of alphanumeric characters, for each fitted line, summing a distance of all other respective rectangular fittings to the respective fitted line, 
 selecting the respective pair of alphanumeric characters corresponding to the respective fitted line with a smallest summed distance of all of the fitted lines as a text baseline for the candidate vehicle license plate image, 
 compute a score for the candidate vehicle license plate image having the selected text baseline based at least on the rectangular fitting around each of the alphanumeric characters, relative positions of each of the alphanumeric characters relative to each other within the respective cropped object image and a calculated slope of the fitted line for the selected pair of alphanumeric characters; and 
 recover, by the processor, information relating to a vehicle license plate in response to the calculated score of the candidate vehicle license plate image confirming that the respective cropped object image corresponds to the vehicle license plate. 
 
 
     
     
       18. The computer program product of  claim 17 , wherein the code to process the captured optical image is configured to process the captured optical image to identify one or more of the object images from the captured optical image, each of said one or more of the object images comprising a candidate vehicle license plate image. 
     
     
       19. The computer program product of  claim 18 , wherein the code for processing the captured optical image is further configured to dewarp at least one of said one or more of the object images. 
     
     
       20. The computer program product of  claim 17 , wherein the code to process the captured optical image is further configured to select said one of the object images from said one or more of the cropped object images based on the scores. 
     
     
       21. The computer program product of  claim 20 , wherein the code to process the captured optical image is further configured to recover the information from the selected one of said one or more of the cropped object images. 
     
     
       22. A mobile apparatus, comprising:
 an image sensor configured to capture an optical image including an image of a vehicle license plate; 
 a timing circuit configured to sample an electrical signal corresponding to the captured optical image at a frame rate; and 
 a license plate detector configured to:
 identify and crop, by a processor, one or more object images as a candidate vehicle license plate from the captured optical image having a plurality of alphanumeric characters, 
 score, by the processor, each of said cropped one or more of the object images based on a probability that the respective cropped object image comprises the vehicle license plate image, wherein each of the cropped one or more object images is scored by:
 providing a rectangular fitting around each character of the plurality of alphanumeric characters, 
 fitting a line to a center of the respective rectangular fittings of each pair of the plurality of alphanumeric characters, 
 for each fitted line, summing a distance of all other respective rectangular fittings to the respective fitted line, 
 selecting the respective pair of alphanumeric characters corresponding to the respective fitted line with a smallest summed distance of all of the fitted lines as a text baseline for the candidate vehicle license plate, 
 computing a score for the candidate vehicle license plate having the selected text baseline based at least on the rectangular fitting around each of the alphanumeric characters, relative positions of each of the alphanumeric characters relative to each other within the respective cropped object image and a calculated slope of the fitted line for the selected pair of alphanumeric characters, and 
 
 recover, by the processor, information relating to the vehicle license plate in response to the calculated score of the candidate vehicle license plate confirming that the respective cropped object image corresponds to the vehicle license plate. 
 
 
     
     
       23. The apparatus of  claim 22 , wherein at least one of said one or more of the object images comprising a candidate vehicle license plate image. 
     
     
       24. The apparatus of  claim 23 , wherein the license plate detector is further configured to process said at least one of the plurality of samples to score each of said one or more of the object images based on a probability that the object image comprises the vehicle license plate. 
     
     
       25. The apparatus of  claim 24 , wherein the license plate detector is further configured to process at least first and second samples of the plurality of samples to score each of said one or more of the object images from each of said at least first and second samples. 
     
     
       26. The apparatus of  claim 25 , wherein each of said one or more object images detected in the first sample is associated with location information, and wherein the license plate detector is further configured to use the location information to estimate the location of said one or more of the object images in the second sample. 
     
     
       27. The apparatus of  claim 24 , wherein the license plate detector is further configured to stop processing the sampled electrical signal when said score is above a threshold value. 
     
     
       28. The apparatus of  claim 20 , further comprising
 a display, wherein each sample represents a frame of a video image presented to the display; and 
 a rendering module configured to render each frame of the video image to the display and overlay a detection indicator on each of said one or more of the cropped object images. 
 
     
     
       29. The apparatus of  claim 28 , wherein the overlay provides a visual indication of the object image associated with the score that is above a threshold value.